Line choke coil



y 1950 M. J. BROWN 2,515,984

LINE CHOKE COIL Filed June 2, 1947 WITNESSES: INVENTOR Nyron Jfiro N22.

2640. W BY ATTOR Y Patented July 18, 15.50

UNITED STATES PATENT OFFICE LINE CHOKE COIL Myron J. Brown, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 2, 1947, Serial No. 751,777

1 2 Claims.

The present invention relates to line choke coils, which are intended to be connected in series ina transmission or distribution line to carry the normal, relatively low-frequency power current, and to interpose a high impedance to high-frequency carrier currents, which may be superimposed on the power current for communication or other purposes. The choke coil of the present invention is particularly suitable for use in connection with carrier current telephone systems on rural lines, although its usefulness is not necessarily restricted to this particular application.

The principal object of the present invention is to provide a line choke coil for outdoor use which is weatherproof and of rugged construction, so as to have long life.

Another object of the invention is to provide a line choke coil for outdoor service which is capable of suspension mounting directly in a line, or which may alternatively be mounted on a separate support by means of a grounded clamp.

A more specific object of the invention is to provide a line choke coil enclosed in an oil-filled porcelain housing and supported on a strain member extending longitudinally through the housing,

so that the coil can be inserted directly in a line with the strain member carrying the stresses imposed by the line conductors. The strain member also carries terminal means for the coil at its ends, and a protective gap device is preferably mounted on the outside of the housing to protect the coil against voltage surges on the line.

Other objects and advantages of. the invention will be apparent from the following detailed description, taken in connection with the accompanying drawing, in which:

Figure 1 is a side View, partly in longitudinal section, showing a choke coil embodying the invention;

Fig. 2 is a view in elevation showing the choke coil inserted directly in a line; and.

Fig. 3 is a similar view showing an alternative manner of mounting the coil.

As shown in Fig. l, the choke coil is contained in a generally cylindrical housing I, which is preferably made of porcelain, and which is provided with circumferential ribs to increase the creepage distancebetween the ends of the housing. The ribs are omitted at the central portion 2 of the housing, however, to leave a smooth,

cylindrical surface, so as to permit mounting the coil by means of a clamp, as described hereinafter. The housing I is preferably completely filled with oil 3, or other suitable insulating liquid, after assembly of the device.

The coil itself is supported on a tubular coil support 4 of rigid insulating material, and consists of a plurality of individual coil sections "5 which are connected in series as indicated at 6. Any necessary number of sections 5 may be utilized, and they are preferably spaced apart, as shown, in order to control the distributed capacitance, so as to obtain the desired impedance at the carrier frequency. It will be apparent that the use of a plurality of spaced coil sections in this manner permits considerable flexibility in the design of the coil, and itcan readily be designed to have very low, or substantially negligible, impedance at the power current frequency, which is usually. sixty cycles per second, and to have very high impedance at the carrier current frequency, which may be of the order of or kilocycles per second, for example.

A strain member is disposed longitudinally in the housing I. The strain member includes a strain rod 1 of any suitable insulating material which has sulficient mechanical strength. The strain rod i is preferably of square cross-section, and its length is somewhat less than the length of the housing I, so that it does not extend all the way to the end of the housing at either end. A substantially U-shaped metal strap 8 issecured to each end of the strain rod 1 by means of rivets 9, the strap 8 at each end extending substantially to the end of the housing I. A nut I0 is secured within the end of the strap member 8 beyond the end of the strain rod 1 by welding, or in any other suitable manner, and a hole is provided in the end of the strap 8 opposite the nut ill. The tubular coil support 4 is carried on the strain rod 'l by means of metal support members i i at each end of the strain rod 1, which may be secured under one of the rivets 9. The coil support 4 is preferably freely supported on the members I I with a sliding fit so as to permit relative axial movement.

The ends of the housing I are closed by metal end caps [2 which are made of relatively thin sheet metal so as to have some flexibility. The periphery of each of the end caps I2 is secured to the end of the housing I and sealed thereto in any suitable manner, preferably by soldering the end cap to a metallic glaze on the end of the housing I, as indicated at l3. A central hole is provided in each end cap 12, and a terminal stud l4 extends through this hole, through the hole in the end of the strap 8, and is threaded into the nut so as to be secured to the end of the strain rod '4. A nut I5 is threaded on the terminal stud It on the outside of the end cap and tightened against the end cap and the strap 8 to rigidly secure the strain member to the end cap at the center of the end cap. The nut I5 is preferably soldered to the end cap after it has been tightened, to prevent subsequent loosening of the nut and to seal the opening to prevent the escape of oil. Thus, the end cap I2 is rigidly secured to the housing 1 at its outer periphery and to the strain rod I at its center. The end cap [2, however, has sufiicient flexibility to permit it to yield and allow thermalexpansion of the oil 3 contained in the housing .I.

The end coil section 5 at each end is connected to the end cap 52 at that end by means of a conductor it, which extends through a small aperturein the end cap and is soldered to the end cap on the'outside to seal the aperture and to insure. a good electrical connection. Thus, the .coil is connected in series between the two metal end caps l2, which, in turn, are electrically connectedto the terminal studs l4 so that the studs serve as terminals for the coil. In use, terminal devices ll of any suitable type may be attached to the studs is by means of nuts is threaded on the studs.

Since the choke coil is to be connected in series in .aline. it is subject to damage by voltage surges on the line resulting from lightning strokes or switching operations. In order to protect the coil against such damage, a protective gap device is provided to by-pass voltage surges. This gap device is preferably mounted on the outside of the housing, and consists of two metal electrodes I9, which may be made of brass. The electrodes I9 are mounted on the terminal studs M and secured in place by nuts :26. As shown in the drawing, each electrode extends radially from the terminal stud past the outer periphery of the housing and then extends axially toward the other electrode, which is secured at the other end of the housing. The opposing ends of the two electrodes are spaced apart to form a gap between them, which is positioned in the center of the housing over the central portion 2, so that the gap is spaced far enough-away from the surface of the housing topreventdamage to the porcelain by the heat of the arc. It will be apparent that the protective gap is connected directly across the coil, and that it willbreak down and by-pass the coil upon occurrence of a predetermined excess voltage to protect th coil against damage. The protective gap is preferably mounted on the outside of the housing l, described, but it will be apparent that the-gap might be placed inside the housing, ii. desired.

The use of the strain member, including the strain rod l, which the coil is supported, and the terminal studs M, makes it possible to suspend the complete coil assembly directly in a line. Thus, the coil is shown in Fig.2 supported between the line conductors 2| and 22. When the coil to be mounted in this manner, screw eyes 23 are threaded on the terminal studs M, and theline conductors 2H and 22 may then be looped through the screw eyes 23, with the ends of the conductors carried to the terminal devices H. In this way, the coil is connected directly in series in the line, and is physically interposed in the line so that no separate supporting structure is required for the coil. The strain rod 1 carries the stresses imposed by the line conductors, so that no great stress is imposed on the coil itself or in the terminal devices. Thus, the construction described makes possible suspension mounting directly in the line.

If it is desired to mount the coil separately from the line, however, this may be done in the manner shown in Fig. 3. When mounted in this manner, the screw eyes 23 are omitted, and

a metal clamp 2c of any suitable type is clamped on the central portion 2 of the housing I. The clamp 25 may then be mounted on a bracket .25, which is secured to a supporting structure 26, such as a line pole or a part of substation structure. Leads from the line may be brought to the terminal devices H to connect the coil in the line.

It should now be apparent that a, line choke coil has been provided which is of rugged and weatherproof construction, so as to be suitable for outdoor use with long life. The coil is protected against voltage surges by means of a protective gap mounted on the housing, and the coil isof oil-filled porcelain-clad construction, with flexible metal end caps which permit thermal expansion of theoil without setting up undue stresses in any part of the assembly. The use of the strain rod l is an important feature of the invention since it makes possible direct suspension mounting of the coil in a line, and thus thecoil hasthe advantage of alternative methods of mounting, .as shown in Figs. 2 and 3.

Apreferred embodiment of the invention has been shown and described for the purpose of illustration, but it will be. apparent that various modifications may be made within the scope of theinvention. It is to be understood, therefore, that the invention is not limited to the specific details of construction shown, but in its broadest aspects, it includes all equivalent embodiments and modifications which come within the scope of the appended claims.

I claim as my invention:

1. A choke coil comprising an insulating housing, a strain rod of insulating material disposed longitudinally-insaidhousing. a tubular coil support mounted on the strainrod, a coil supported on the coilsuphort, said coil comprising a plu' rality cf series-connected multi-turn sections spaced apart longitudinally of the coil support, metal end caps closing and sealing the ends of the housing, metal terminal members secured to the ends of the strain rod within the housing, said terminal members extending through the end caps and being joined thereto, meansfor electrically connecting the ends of said coil to the end caps, and an insulating liquidliillmgthe housing.

2. A. choke coil comprising an insulating housing, a strain rod. of. ,insulatingmaterial disposed longitudinally insaid housing, a tubular coil support mounted on the strain rod, a coil supported on the coil support, said coil comprising .a plurality of series-connected multi-turn sections spaced apart longitudinally of the coil support, metal endcaps closing and sealing the endsof the housing, metal terminal members secured to the ends of the strain rod within the housing, said terminal members extending through the end caps and being joined thereto, means for electrically connecting the ends of said coil to the end caps, an insulating liquid filling the housing, and electrode members mounted on the terminal members outside the housing, said electrode members extending radially of the end caps and longitudinally of the housing to form a, spark gap between them intermediate the ends of the housing, said spark gap being spaced from the surface of the housing.

MYRON J. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Number Name Date Chernyshoff Jan. 9, 1917 Jackson Feb. 27, 1917 Jackson July 2, 1918 Replogle Feb. 8, 1921 Dill June 26, 1923 Steinberger Apr. 8, 1924 Thordarson May 17, 1927 Newton May 17, 1927 Ready Feb. 4, 1930 Amy July 25, 1933 Capart Apr. 2, 1935 FOREIGN PATENTS Country Date Great Britain July 2, 1928 

